Applicants claim priority under 35 U.S.C. xc2xa7119 of German Application No. 101 61 276.1-16 filed Dec. 14, 2001.
1. Field of the Invention
The present invention relates to an elastic film laminate, made of at least two connected plastic films, including a first film and at least one other, second film. The first film is elastomeric in at least one direction, can be reversibly stretched by a length xcex94lA during a deformation and demonstrates no or only a very slight residual deformation xcex94la. The second film is made of a deformable plastic material, which is connected with the first film in localized connection regions, but not over its entire area. The second film has received a permanent deformation xcex94lb which is significantly greater than the deformation xcex94la, by means of a common deformation by a length xcex94lA, so that the film material of the second film is permanently deformed between the localized connection regions, forming, for example, small arches and bulges.
2. The Prior Art
A film laminate of the type indicated above is known from the European Patent 0 646 062. This patent describes an elastic film laminate that has a continuous elastomer core layer and at least one continuous and elastic outside skin layer made of oriented plastic, whereby the elastomer core layer is essentially in continuous contact with the skin layer. The multi-layer laminate is stretched beyond the elasticity limit of the skin layer in one working step, causing it to be deformed. The stretched, multi-layer laminate is heated in selected regions, resulting in a random arrangement of the elastic laminate in these regions.
A bulked material is thereby obtained by means of a very complicated process. However, nothing is said in this European patent concerning how the material of the outside skin layer acts when it is stretched further, beyond the threshold value that results after stretching of the bulked regions. Usually, the tear limit is quickly reached, so that the material is destroyed, at least with regard to its outside layers.
The object of the invention is to provide an elastic film laminate with a similar structure as that of the state of the art, but which has different properties which are achieved by means of the selection of the materials. In particular, the object is to provide an elastic film laminate which does not have a tendency to tear if the aforementioned threshold value is exceeded, and which exhibits specific stress-strain diagrams.
In accordance with the invention, an elastic film laminate is provided which is made of at least two laminated plastic films, including a first film and at least one other, second film made of a deformable plastic material, which is connected with the first film in localized connection regions, but not over its entire area. The first film is elastomeric in at least one direction, can be reversibly stretched by a length xcex94lA during a deformation, and demonstrates no or only a very slight residual deformation xcex94la. The second film has received a permanent deformation xcex94lb, which is significantly greater than the deformation xcex94la, by means of a common deformation by a length xcex94lA, so that the material of the second film is permanently deformed between the localized connection regions, forming, for example, small arches and bulges. In case of a renewed deformation of the film laminate according to the invention, above the limit range of deformation, where xcex94l greater than xcex94lA applies, the tensile force required for further stretching of the laminate increases suddenly because of the reaction force of the second film that becomes effective at this stretching force. In addition, in the laminate according to the invention, the tear resistance of the second film is adjusted so that if the tensile force is increased further, at least stretching of 10% of its length is still possible beyond xcex94lA until tear.
With the laminate film according to the invention, sufficient strength is achieved, particularly in the case of elastic closure bands, such as those used for hygiene articles, without having to use comparatively thick elastomer films, which require higher material costs and also have only a limited ability to stretch within the elastic range.
In the case of thick films, the stretching force is also very great, so that the use of such a product is made more difficult.
The laminate films according to the invention are produced from one or more elastomer films and from one or more films that are capable of stretching. To produce such laminate film, no complicated production methods are required. The films of the laminate are selected so that the elastomer film with the smallest degree of permanent deformation determines the elastic behavior in the first stretching range.
If a second elastic range should be desirable for a particular use, a second elastomer film is used in the laminate, which has a higher degree of permanent deformation. According to a preferred embodiment, a film laminate is provided which has two second films. The two second films are connected, directly or indirectly, with the first film only in localized regions and have different degrees of permanent deformation. In the case of a renewed deformation of the film laminate, above the limit range of deformation, where xcex94l greater than xcex94lA applies, the tensile force required for further stretching of the laminate increases suddenly because of the reaction force of the second films that becomes effective at this stretching force. The tear resistance of the second films is adjusted so that if the tensile force is increased further, at least stretching of 10% and 20% of their length, respectively, is still possible beyond xcex94lA until tear, whereby one second film has a degree of deformation that is at least 10% higher than that of the other after the first stretching process, so that when repeated stretching of the film laminate composed of the two second films and one first film occurs, two gradations of the stress-strain diagram can be observed.
For additional elastic regions, additional layers and films can generally be used. In this manner, it is possible to compose laminates as desired, which demonstrate different stretching forces and restoring forces in different service regions. The elasticity behavior can be defined as needed, in different regions, by selecting known films. Even the overall strength that is important for elastic closure bands can be determined by using one or more stretchable plastic layers. After having been processed to produce a film laminate, this layer does not limit the elasticity in the desired region, but rather adds an ability of the laminate. This function can be fulfilled by one or several stretchable layers.
In particular, the elastomer film should demonstrate a permanent deformation xcex94lA of a maximum of 10% of the original length when stretched by 175% of the original length.
In this connection, above the stretching distance xcex94l greater than xcex94lA, the tensile force required for the same amount of stretching should preferably be greater for the second film than for the first film.
The first film preferably consists of an elastomer, selected from among the group of styrene block copolymers, polyurethanes, polyesters, polyethers, or polyester block copolymers.
The second, non-elastomer films consist, for example, preferably of a stretchable polyolefin, particularly of polyethylene, its copolymers, or of polypropylene, its copolymers, or of mixtures of the aforementioned polyolefins.
The connections between the films, relative to one another, can be produced by means of heat-bonding, preferably under pressure, or by means of gluing using adhesives, particularly by means of hot-melt glues.
The film layers can also be covered with fiber nonwoven fabrics or textile knitted or woven fabrics on at least one side.
It is also possible to perforate the film laminate, in order to increase the air permeability.